Related subject matter is disclosed in a co-pending U.S. patent application of John R. Baldwin et al., filed on Nov. 28, 2000, Ser. No. 09/722,423, entitled xe2x80x9cFault Interrupter Using Microprocessor for Fault Sensing and Automatic Self-Testingxe2x80x9d, the entire contents of said application being expressly incorporated herein by reference.
The present invention relates generally to a fault interrupting device, such as a ground fault circuit interrupter or an arc fault circuit interrupter.
Fault interrupting devices are designed to trip in response to the detection of a fault condition at an AC load. The fault condition can result when a person comes into contact with the line side of the AC load and an earth ground at the same time, a situation which can result in serious injury. A ground fault circuit interrupter (GFCI) detects this condition by using a sense transformer to detect an imbalance between the currents flowing in the line and neutral conductors of the AC supply, as will occur when some of the current on the line side is being diverted to ground. When such an imbalance is detected, a relay or circuit breaker within the GFCI device is immediately tripped to an open condition, thereby removing all power from the load. Many types of GFCI devices are capable of being tripped not only by contact between the line side of the AC load and ground, but also by a connection between the neutral side of the AC load and ground. The latter type of connection, which may result from a defective load or from improper wiring, is potentially dangerous because it can prevent a conventional GFCI device from tripping at the intended threshold level of differential current when a line-to-ground fault occurs.
A ground fault is not the only class of potentially dangerous abnormal operating conditions. Another type of undesirable operating condition occurs when an electrical spark jumps between two conductors or from one conductor to ground. This spark represents an electrical discharge through the air and is objectionable because heat is produced as an unintentional by-product of this unintentional xe2x80x9carcingxe2x80x9d path. Such arcing faults are a leading cause of electrical fires. Arcing faults can occur in the same places that ground faults can occur; in fact, a ground fault would be called an arcing fault if it resulted in an electrical discharge, or spark, across an air gap. A device known as an arc fault circuit interrupter (AFCI) can prevent many classes of arcing faults.
Some GFCI devices employ a microprocessor in conjunction with a conventional GFCI chip to perform self-testing functions. These GFCI devices typically provide distinct functions for each I/O port of the microprocessor. However, maximum temperature rise requirements are in place requiring the maximum temperature rise requirement to be lower in GFCI and AFCI devices. In order to meet these requirements while maintaining a low cost device, a need exists for a microprocessor within the GFCI or AFCI device to be able to receive a plurality of different inputs at a single I/O port of the microprocessor. By requiring fewer I/O ports, a smaller microprocessor can be used and heat dissipation can be reduced.
Additional UL requirements allow for a maximum time period within which the load must be disconnected from the power supply in the event of a ground fault or arc fault. Some conventional GFCI and AFCI devices disconnect the load by de-energizing a solenoid to open contacts that had previously coupled the load to the AC supply. However, this arrangement dissipates excessive heat and may not be capable of opening the contacts within the time prescribed. Accordingly, a need exists for a novel circuit which continuously energizes the solenoid to maintain the contacts in a closed position, without generating excessive heat in the device.
Although GFCI and AFCI devices can provide useful protection against electrical hazards, they may inadvertently create potentially dangerous situations. For example, if a ground fault circuit interrupter is inadvertently powered through its load or feed-through terminals rather than through its line or input terminals, the GFCI will trip normally when confronted with a ground fault condition but the load plugged into the GFCI receptacle will not be disabled. The miswiring may not be detected because electrical power is usually provided to the GFCI face receptacles some time after installation. Accordingly, the GFCI will remain incorrectly wired unless the installer is able to immediately detect the miswiring condition. Therefore, a need exists for a device that removes power from a receptacle coupled to a GFCI or AFCI, as well as all downstream receptacles, in the event that a miswiring condition occurs.
According to one aspect of the present invention, a fault interrupter comprises a first and second input terminals for connection to the line and neutral terminals, respectively, of a power source; first and second output terminals for connection to the line and neutral terminals, respectively, of a load; and first and second conductive paths extending, between the first and second input terminals and the first and second output terminals; first and second contact sets for completing and interrupting the first and second conductive paths, respectively; an actuator for operating the first and second contact sets; and a first and second electronic switching device coupled to the actuator, the first electronic switching device being adapted to energize the actuator for a selected period of time, the second electronic switching device being adapted to energize the actuator after the first electronic switching device ceases operation.
In accordance with a second aspect of the present invention provides a fault interrupter apparatus comprises first and second input terminals for connection to the line and neutral terminals, respectively, of a power source; first and second output terminals for connection to the line and neutral terminals, respectively, of a load; first and second conductive paths extending, between the first and second input terminals and the first and second output terminals; first and second contact sets for completing and interrupting the first and second conductive paths, respectively; a fault sensing circuit adapted to produce a fault signal in response to the detection of a fault condition at the load; and a processing device coupled to an output of the fault sensing circuit for receiving the fault signal and for operating the first and second contact sets to open the respective first and second conductive paths.
In accordance with a third aspect of the present invention, a fault interrupter apparatus comprises first and second input terminals for connection to the line and neutral terminals, respectively, of a power source; first and second output terminals for connection to the line and neutral terminals, respectively, of a load; first and second conductive paths extending, between the first and second input terminals and the first and second output terminals; first and second contact sets for completing and interrupting the first and second conductive paths, respectively; and a processing device for operating the first and second contact sets in response to a plurality of input signals, wherein a single input of said processing device is adapted to receive more than one of said input signals.
In accordance with a fourth aspect of the present invention a fault interrupter apparatus comprises first and second input terminals for connection to the line and neutral terminals, respectively, of a power source; first and second output terminals for connection to the line and neutral terminals, respectively, of a load; first and second conductive paths extending, between the first and second input terminals and the first and second output terminals; first and second contact sets for completing and interrupting the first and second conductive paths, respectively; and a controller for operating the first and second contact sets in response to the detection of a fault condition at the load, the controller being operative to periodically open the first and second contact sets, to monitor a voltage at the load to verify that the first and second contact sets have opened, and to re-close the first and second contact sets after a predetermined period of time after verifying that the first and second contact sets have re-closed, the predetermined period of time being extended by the controller if the first and second contact sets have not re-closed within the predetermined period of time.
The present invention is also directed to methods which can be used in connection with the fault interrupting apparatus described above.